With the booming of the Wimax (World Interoperability for Microwave Access), to maintain the competence of the third generation mobile communication system in the field of mobile communication, it is necessary to improve its network performance and reduce its cost for network construction and operation. Therefore, the standardization working groups of the 3GPP (3rd Generation Partnership Project) are currently working at researching the evolution of the PS Core (Packet Switch Core) and the UTRAN (Universal Mobile Telecommunication System Radio Access Network), and this topic of this research is called the SAE (System Architecture Evolution), which aims at enabling the EPC (Evolved Packet Core) to provide a higher transmission rate and a shorter transmission delay, to optimize packeting and to support mobility management among the E-UTRAN (Evolved UTRAN), the UTRAN, the WLAN (Wireless Local Area Network) and other non-3GPP access networks.
FIG. 1 illustrates a current SAE system comprising the following network elements:
an E-RAN (Evolved RAN): providing higher uplink and downlink rates, a lower transmission delay and more reliable wireless transmission. The E-RAN includes network elements of eNodeB (Evolved NodeB) which provides wireless resources for user access.
A PDN (Packet Data Network): a network providing services to the users.
An MME (Mobility Management Entity): a control plane functional entity, a server which temporarily stores user data, in charge of managing and storing UE (User Equipment) context (such as UE identifier, mobility management state and user security parameters), assigning a temporary identifier for a UE, in charge of authenticating a UE residing in its tracking area or network; processing all non-access-stratum messages between the MME and the UE; triggering the paging in the SAE. The MME is a mobility management unit of the SAE system.
A serving GW (Gateway): the Serving GW is a user plane entity, in charge of user plane data route processing, buffering the downlink data sent to the UE in an idle state, managing and storing the SAE bearer contexts of the UE, such as IP bearer service parameters and network internal route information. The Serving GW is an anchor point of the user plane in the 3GPP system, and one user can only have one Serving GW at a certain moment.
A PDN GW: a gateway in charge of accessing the UE to the PDN, assigning an IP address for the UE, being also a mobility anchor point of the 3GPP and non-3GPP access systems, and the functions of the PDN GW further comprise policy enforcement and charging support. The UE can access multiple PDN GWs at the same moment. A PCEF (Policy and Charging Enforcement Function) is also located in the PDN GW.
A PCRF (Policy and Charging Rules Function): in charge of providing policy control and charging rules to the PCEF.
An HSS (Home Subscriber Server): permanently storing user subscribing data, the contents stored by the HSS comprise the IMSI (International Mobile Subscriber Identification) of the UE, the IP address of the PDN GW, the AMBR (Aggregate Maximum Bit Rate) corresponding to the PDN GW which is accessible to the users, and etc.
Physically, the Serving GW and the PDN GW may be integrated as one. The EPC system user plane network elements comprise the Serving GW and the PDN GW.
In the SAE system, the Serving GW has the function of buffering downlink data sent by the PDN GW to the UE which is in the idle state. When the UE is in the idle state, the Serving GW does not store therein the address and tunnel information of the eNodeB, when receiving the downlink data sent by the PDN GW to the UE, the Serving GW needs to buffer it and send a data notification message (Downlink Data Notification) to the MME; and the MME pages the UE. If the MME receives a paging response of the UE, the processing of a Service Request is performed, and in this process the MME informs the eNodeB of the Serving GW's address and tunnel information and informs the Serving GW of the eNodeB's address and tunnel information, thereby a data transmission tunnel on the S1 interface is established. The Serving GW sends the buffered data to the eNodeB via the tunnel, and the specific transmission flow is shown in FIG. 2 as follows:
Step 201, when the downlink data sent to the UE reaches the PDN GW, the PDN GW uses an existing bearer to route the received downlink data to the Serving GW;
Step 202, after receiving the downlink data, the Serving GW judges whether the address information and the tunnel information of the eNodeB to which the UE belongs are stored, if they are not stored, the Serving GW buffers the received downlink data which are sent to the UE and sends a data notification message to the MME;Step 203, after receiving the data notification message, the MME initiates, according to a stored user location information Tracking Area List, paging requests to all eNodeBs in the user location information Tracking Area List, and starts a paging timer;Step 204, the eNodeBs that have received the paging request page the UE at an air interface;Step 205, when receiving the paging from a certain eNodeB, the UE sends a service request message to the eNodeB that has successfully paged the UE;Step 206, after receiving the service request message, the eNodeB that has successfully paged the UE forwards the service request message to the MME;Step 207, after receiving the service request message, the MME turns off the paging timer and sends a bearer establishment request to the eNodeB that has successfully paged the UE, and carries in the bearer establishment request the address information of the Serving GW, the uplink tunnel information at the Serving GW side of S1 interface of all the bearers and QoS (Quality of Service) information of all the bearers;The address information of the Serving GW, the uplink tunnel information at the Serving GW side of S1 interface of all the bearers and the QoS (Quality of Service) information of all the bearers are stored in the MME by the UE in the idle state;Step 208, after receiving the bearer establishment request, the eNodeB that has successfully paged the UE stores the uplink tunnel information at the Serving GW side of S1 interface of all the bearers, assigns air interface resources for them according to the QoS of the bearers, and initiates a radio bearer establishment request to the UE;Step 209, after receiving the radio bearer establishment request, the UE performs establishment of radio bearers, and returns a radio bearer establishment response to the eNodeB that has successfully paged the UE after finishing the establishment of the radio bearers;Step 210, after the eNodeB that has successfully paged the UE receives the radio bearer establishment response, the air interface portions of all the bearers have been successfully established, the eNodeB assigns downlink tunnel information to the S1 interface of all the bearers and returns a bearer establishment response to the MME, and the bearer establishment response carries therein the downlink tunnel information of the S1 interface of all the assigned bearers;Step 211, after receiving the bearer establishment response, the MME initiates an update bearer request to the Serving GW for each bearer, and the update bearer request carries therein the downlink tunnel information of the S1 interface assigned for the bearer by the eNodeB that has successfully paged the UE and the address information of the eNodeB that has successfully paged the UE;Step 212, after receiving the bearer establishment response, the Serving GW stores the downlink tunnel information of the S1 interface of the bearer and returns an update bearer response to the MME; a S1 data transmission tunnel between the eNodeB and the Serving GW is now established; andStep 213, the Serving GW sends to the UE the buffered data using the S1 data transmission tunnel and the air interface as established.
Through the above process, all the bearers of the user are activated, and the user and the PDN GW can transmit uplink and downlink data via all the bearers.
The problem at present lies in that the response for the paging of the UE can possibly not be obtained (for example, the user takes off the battery and thus cannot respond to the paging message), and at this time the Serving GW needs to release the buffered data. A current solution is to set a timer in the Serving GW for each UE to which paging has been triggered, and if the update bearer request of the MME is not received within a timing period (the above step 211), the Serving GW will release the buffered data. However, this solution has a disadvantage that the timing period of the timer in the Serving GW cannot be shorter than that of the paging timer in the MME, otherwise a problem will occur that the UE successfully responds to the paging while the Serving GW releases the buffered data; however, if the timing period of the timer of the Serving GW is longer than that of the paging timer of the MME, the buffered data of the Serving GW cannot be released in time, with a result that system resources are wasted and processing efficiency is lowered.